介绍:JS函数中的代码会被函数被invoke(调用)时执行.
函数被定义时代码不执行,
函数调用时函数内的代码会被执行.
常用的term是 call a function 而不是 invoke a function.
function always belong to a object in javascript.
When a function does no tbelong to nay object. In javascript there is alaways a default global object.
在Html 中,是浏览器窗口本身. the global object will become a window function in this case.
That means it can be invoked by window.functionName().
1. this keyword : 代表当前代码的对象.
The value of this, when used in a function , is the objec that owns the function.
Note that this is not a variablke. It is a keyword. You cannot change the value of this.
2. Invoking a Function as a Method
In javascript you can defiune functions as object methods.(对象方法?),形如:
var myObject = {
firstName:"John",
lastName: "Doe",
fullName: function () {
return this.firstName + " " + this.lastName;
}
}
myObject.fullName(); // Will return "John Doe"
3. 对于JSON对象,可以使用"."来调用对象内方法.
var myObject = {
firstName:"John",
lastName: "Doe",
fullName: function() {
return this.firstName+" "+this.lastName;
}
}
4.Invoking a Function with a Function Constructor
NOTE:
A constructor invocation creates a new object. The new object inherits the properties and methods from its constructor.
The this keyword in the constructor does not have a value.
The value of this will be the new object created when the function is invoked.
====================================Call==================================
All Functions are Methods:If a function is not a method of a JavaScript object, it is a function of the global object (see previous chapter).
1. The JavaScript call() method.
2. The call() method with Arguments.
Output:
John Doe,Oslo,Norway
=======================apply()=================
和call()方法类似.
区别是,call() 的参数是分隔开的, apply()的参数是一个数组.
person.fullName.call()变成了person.fullName.apply(person1,["Oslo","Norway"]);
====实例 Math.max(arg1,arg2,arg....)
Math.max(1,2,3);会返回3
但是JavaScript数组并没有max()方法,所以可以apply Math.max()方法.
Math.max.apply(null, [1,2,3]); // Will also return 3
第一个参数(null)无关紧要.在本例中不使用.